Pulsating B-type stars in the open cluster NGC 884: frequencies, mode identification and asteroseismology

TL;DR

This study conducts a detailed asteroseismic analysis of B-type stars in the open cluster NGC 884, identifying pulsation modes and estimating the cluster's age through ensemble asteroseismology.

Contribution

It provides the first comprehensive frequency and mode identification for multiple B-type stars in NGC 884, demonstrating the potential of ensemble asteroseismology for cluster age determination.

Findings

Detected 115 frequencies across 65 stars.

Identified pulsation modes for 12 frequencies in 9 stars.

Estimated cluster age as log(age/yr)=7.12-7.28.

Abstract

Recent progress in the seismic interpretation of field beta Cep stars has resulted in improvements of the physics in the stellar structure and evolution models of massive stars. Further asteroseismic constraints can be obtained from studying ensembles of stars in a young open cluster, which all have similar age, distance and chemical composition. We present an observational asteroseismology study based on the discovery of numerous multi-periodic and mono-periodic B-stars in the open cluster NGC 884. We describe a thorough investigation of the pulsational properties of all B-type stars in the cluster. Overall, our detailed frequency analysis resulted in 115 detected frequencies in 65 stars. We found 36 mono-periodic, 16 bi-periodic, 10 tri-periodic, and 2 quadru-periodic stars and one star with 9 independent frequencies. We also derived the amplitudes and phases of all detected frequencies in the U, B, V and I filter, if available. We achieved unambiguous identifications of the mode degree for twelve of the detected frequencies in nine of the pulsators. Imposing the identified degrees and measured frequencies of the radial, dipole and quadrupole modes of five pulsators led to a seismic cluster age estimate of log(age/yr) =7.12-7.28 from a comparison with stellar models. Our study is a proof-of-concept for and illustrates the current status of ensemble asteroseismology of a young open cluster.